1. Field of the Invention
This invention relates to a differential mechanism of a four-wheel driving apparatus for vehicles, and more particularly to a differential mechanism of a four-wheel driving apparatus for vehicles having a free range and a lock range.
2. Description of the Prior Art
FIG. 5 shows a conventional differential mechanism of a four-wheel driving apparatus for vehicles. In FIG. 5, an input torque is transmitted from an input shaft 1 to a carrier 2 and transferred from a pinion gear 3 to a ring gear 4 and a sun gear 5 and is transmitted to a front wheel output shaft 6 via the ring gear 4 and a rear wheel output shaft 7 via the sun gear 5. A gear 9 is integrally rotatable with the front wheel output shaft 6 and a gear 10 is integrally rotatable with the rear wheel output shaft 7. The gears 9 and 10 are operatively connected by sliding a sleeve 8 mounted on a rear side of the differential planetary gear into one direction so that the front wheel output shaft 6 and the rear wheel output shaft 7 are connected or locked with each other.
Japanese Utility Model Laid Open Letter No. 60 (1985)-69726 is an example of a conventional differential mechanism of a four-wheel driving apparatus for vehicles. Therein, the ring gear 4 and the sun gear 5 are in a locked or connected state along the teeth surface in the four-wheel driving apparatus and torque transmission is always transmitted between each gear. Therefore, durability and strength of the gears has to be maintained during low range operation of the four-wheel drive due to large torque transmission. As a result, each gear is required to be large in size and heavy in weight. Further, the sleeve 8 is located at a rearward position of the differential planetary for changing between the two ranges of lock for four-wheel drive so that the differential mechanism becomes axially longer in order to accommodate the length of the sleeve 8. As a result, it has been extremely difficult to minimize the size of the differential mechanism.
Furthermore, as the differential planetary gear was a single pinion type, the torque distribution to the front wheel output shaft 6 and the rear wheel output shaft 7, i.e., the torque distribution to the ring gear 4 and the sun gear 5 was unbalanced in a ratio of about 7:3.